The present invention relates generally to surgical procedures for spinal stabilization and more specifically to instrumentation adapted for inserting a spinal implant within the intervertebral disc space between adjacent vertebra. More particularly, while aspects of the invention may have other applications, the present invention is especially suited for disc space preparation and implant insertion into a disc space from an anterior surgical approach to the spine.
Various surgical methods have been devised for the implantation of fusion devices into the disc space. Both anterior and posterior surgical approaches have been used for interbody fusions. In 1956, Ralph Cloward developed a method and instrumentation for anterior spinal interbody fusion of the cervical spine. Cloward surgically removed the disc material and placed a tubular drill guide with a large foot plate and prongs over an alignment rod and then embedded the prongs into adjacent vertebrae. The drill guide served to maintain the alignment of the vertebrae and facilitated the reaming out of bone material adjacent the disc space. The reaming process created a bore to accommodate a bone dowel implant. The drill guide was thereafter removed following the reaming process to allow for the passage of the bone dowel which had an outer diameter significantly larger than the reamed bore and the inner diameter of the drill guide. The removal of the drill guide left the dowel insertion phase completely unprotected.
More recent techniques have advanced this concept and have provided further protection for sensitive tissue during disc space preparation and dowel insertion. Such techniques have been applied to an anterior approach to the lumbar spine.
An initial opening or openings are made in the disc space and the height of the disc space is distracted to approximate normal height. Typically, a first distractor is inserted with a height estimated by radiological examination. If additional distraction is required, the first distractor is removed and a second, larger distractor is inserted. However, since the positioning of the distractors is performed without the benefit of protective guide sleeves, the switching of distractors increases the potential for damage to neurovascular structures and may correspondingly increase the time of the procedure.
For bilateral procedures, a double barrel sleeve may be inserted over the distractors, with a central extension extending into the disc space to maintain distraction. One limitation on guide sleeve placement is the amount of neurovascular retraction that must be achieved to place the guide sleeves against the disc space. For some patients, a double barrel sleeve may not be used because there is insufficient space adjacent the disc space to accept the sleeve assembly. Thus, there remains a need for guide sleeves requiring less neurovascular retraction for proper placement and providing greater protection to adjacent tissue.
While the above-described techniques are advances, improvement is still needed to reduce the procedure time by utilization of improved instruments and techniques, to reduce the potential for damage to sensitive tissue adjacent the disc space, and to limit the amount of vessel retraction necessary to utilize the protective instrumentation. The present invention is directed to this need and provides more effective methods and instrumentation for achieving the same.